1. Field of the Invention
The present invention is related to a lighting device that estimates input electric power, a lighting apparatus using the lighting device, and a lighting system.
2. Description of the Related Art
Conventionally, a power source apparatus has been proposed that measures input electric power (power consumption) and presents the measurement result to the outside while converting electric power that is supplied from an external power source as appropriate and supplying the electric power to a load. The measurement result of the input electric power that is obtained from such a power source apparatus is presented to a user of the power source apparatus, an administrator of a facility in which the power source apparatus is installed, etc., so that it is possible to help reduction (saving) of wasted power consumption, etc.
In a light source load using a light emitting diode (LED), which has attracted attention in recent years, the impedance is changed depending on the ambient temperature due to the temperature characteristic. In view of this point, a lighting device is known that tries to obtain input electric power sufficiently accurately even when the ambient temperature of the light source load varies, and for example, is disclosed in Japanese patent laid-open publication No. 2012-074156.
The lighting device that is disclosed in the above-described related art includes an electric power conversion unit configured to adjust electric power that is supplied to a light source load by an ON/OFF operation of a switching element and a control unit configured to input an electric power setting value that is used to determine the size of the electric power that is supplied to the light source load and control an operation of the electric power conversion unit. In addition, the lighting device includes a current detection unit configured to detect current that flows through the switching element and an electric power estimation unit configured to estimate input electric power using the value that is detected by the current detection unit. The electric power estimation unit corrects a portion of variation in a current detection value, which is generated due to change in the ambient temperature of the light source load, using the electric power setting value and the current detection value that corresponds to an output of the current detection unit, and obtains the input electric power.
In particular, in the electric power estimation unit, the electric power setting value is normalized using the electric power setting value when electric power that is supplied to the light source load becomes maximum, as a maximum electric power value, and the input electric power is obtained using an electric power adjustment value that corresponds to a difference between the electric power setting value and the current detection value.
In the conventional example that is disclosed in the above-described related art, it is necessary that the maximum electric power value of the light source load be stored in advance in order to obtain the input electric power. Therefore, for a certain light source load the maximum electric power value of which is stored, the input electric power can be obtained sufficiently accurately, and on the other hand, for another light source load having a different characteristic, there has been a problem in that the input electric power cannot be obtained sufficiently accurately due to variation in characteristics of light source loads.